Boonlakhorn J.,Khon Kaen University |
Kidkhunthod P.,111 University avenue |
Thongbai P.,Khon Kaen University
Journal of the European Ceramic Society | Year: 2015
A novel strategy to improve the dielectric properties of CaCu3Ti4O12 ceramics was proposed by co-doping with Sm3+ and Mg2+. Sm3+ substituted in Ca2+ sites can effectively suppress the grain growth, achieving a fine grained ceramic microstructure. Mg2+ was selected to be substituted into Cu2+ sites to enhance the grain boundary (GB) resistivity for reducing the loss tangent (tanδ). High dielectric permittivity ε'≈1.25×104 and low tanδ≈0.039 at 1kHz were successfully accomplished in a Ca0.925Sm0.05Cu2.70Mg0.30Ti4O12 ceramic. Non-Ohmic properties were also enhanced. A slight increase in Ti3+/Ti4+ ratio in (Sm+Mg) co-doped CaCu3Ti4O12 ceramics was confirmed by the X-ray absorption near edge structure. Changes in tanδ values for all the co-doped ceramics were very consistent with their variations in GB resistance. The dielectric and non-Ohmic properties of co-doped ceramics were significantly improved by tuning both the geometric and intrinsic factors, i.e., increasing the density of GB layer and enhancing the GB resistance, respectively. © 2015 Elsevier Ltd.
Songsiriritthigul C.,111 University avenue |
Buranabanyat B.,Suranaree University of Technology |
Haltrich D.,University of Natural Resources and Life Sciences, Vienna |
Yamabhai M.,Suranaree University of Technology
Microbial Cell Factories | Year: 2010
Background: Mannans are one of the key polymers in hemicellulose, a major component of lignocellulose. The Mannan endo-1,4-β-mannosidase or 1,4-β-D-mannanase (EC 188.8.131.52), commonly named β-mannanase, is an enzyme that can catalyze random hydrolysis of β-1,4-mannosidic linkages in the main chain of mannans, glucomannans and galactomannans. The enzyme has found a number of applications in different industries, including food, feed, pharmaceutical, pulp/paper industries, as well as gas well stimulation and pretreatment of lignocellulosic biomass for the production of second generation biofuel. Bacillus licheniformis is a Gram-positive endospore-forming microorganism that is generally non-pathogenic and has been used extensively for large-scale industrial production of various enzymes; however, there has been no previous report on the cloning and expression of mannan endo-1,4-β-mannosidase gene (manB) from B. licheniformis.Results: The mannan endo-1,4-β-mannosidase gene (manB), commonly known as β-mannanase, from Bacillus licheniformis strain DSM13 was cloned and overexpressed in Escherichia coli. The enzyme can be harvested from the cell lysate, periplasmic extract, or culture supernatant when using the pFLAG expression system. A total activity of approximately 50,000 units could be obtained from 1-l shake flask cultures. The recombinant enzyme was 6 × His-tagged at its C-terminus, and could be purified by one-step immobilized metal affinity chromatography (IMAC) to apparent homogeneity. The specific activity of the purified enzyme when using locust bean gum as substrate was 1672 ± 96 units/mg. The optimal pH of the enzyme was between pH 6.0 - 7.0; whereas the optimal temperature was at 50 - 60°C. The recombinant β-mannanase was stable within pH 5 - 12 after incubation for 30 min at 50°C, and within pH 6 - 9 after incubation at 50°C for 24 h. The enzyme was stable at temperatures up to 50°C with a half-life time of activity (τ1/2) of approximately 80 h at 50°C and pH 6.0. Analysis of hydrolytic products by thin layer chromatography revealed that the main products from the bioconversion of locus bean gum and mannan were various manno-oligosaccharide products (M2 - M6) and mannose.Conclusion: Our study demonstrates an efficient expression and secretion system for the production of a relatively thermo- and alkali-stable recombinant β-mannanase from B. licheniformis strain DSM13, suitable for various biotechnological applications. © 2010 Songsiriritthigul et al; licensee BioMed Central Ltd.
Kulworawanichpong T.,111 University avenue
International Journal of Electrical Power and Energy Systems | Year: 2010
This paper presents a simplified version of the well-known Newton-Raphson power-flow solution method, which is based on the current balance principle to formulate a set of nonlinear equations. Although there exist several powerful power flow solvers based on the standard Newton-Raphson (NR) method, their corresponding problem formulation is not simple due to the need for calculation of derivatives in their Jacobian matrix. The proposed method employs nonlinear current mismatch equations instead of the commonly-used power mismatches to simplify overall equation complexity. Derivation of Jacobian matrix's updating formulae is illustrated in comparison with those of the standard Newton-Raphson method. To demonstrate its use, a simple 3-bus power system was selected as a numerical example. The effectiveness of the proposed method was examined by computer simulations through five test systems: (1) 5-bus test system, (2) 6-bus test system, (3) 24-bus IEEE test system, (4) 30-bus IEEE test system and (5) 57-bus IEEE test system. Its convergence and calculation time were observed carefully and compared with solutions obtained by the standard NR power flow method. The results show that the proposed NR method spends less execution time than the standard method does with similar convergence characteristics. © 2009 Elsevier Ltd. All rights reserved.
Kanjanachuchai S.,Chulalongkorn University |
Euaruksakul C.,111 University avenue
Crystal Growth and Design | Year: 2014
The nucleation and dynamics of multiple generations of In droplets formed from Langmuir evaporation of InP (001), (111)A, and (111)B surfaces are reported. In situ mirror electron microscopy reveals that the majority of first-generation, or mother, droplets break up immediately before they run from the nucleation sites, leaving behind daughter droplets and etch trails where more droplets emerge. These subsequent droplets grow with time and run once a critical size is reached. The breakup and running characteristics are explained in terms of crystallography, viscosity, chemical potential, and temperature and will likely affect the growth processes and designs of various droplet-catalyzed nanostructures and devices. © 2013 American Chemical Society.
Poo-Arporn Y.,111 University avenue |
Thachepan S.,Kasetsart University |
Palangsuntikul R.,King Mongkuts University of Technology Thonburi
Journal of Synchrotron Radiation | Year: 2015
Evidence of internal sulfate attack in field exposure was demonstrated by the damaged interior wall of a three-year-old house situated in Nakhon Ratchasima Province, Thailand. Partial distension of the mortar was clearly observed together with an expansion of a black substance. Removal of the black substance revealed a dense black layer. This layer was only found in the vicinity of the damaged area, suggesting that this black material is possibly involved in the wall cracking. By employing synchrotron-based X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) techniques, the unknown sample was chemically identified. The S 2p and O 1s XPS results mutually indicated the existence of sulfate species in the materials collected from the damaged area. The XANES results indicated the presence of ferrous (II) sulfate, confirming sulfate-induced expansion and cracking. The sulfate attack in the present case appeared to physically affect the structure whereas the chemical integrity at the molecular level of the calcium silicate hydrate phase was retained since there was a lack of spectroscopic evidence for calcium sulfate. It was speculated that internal sulfate probably originated from the contaminated aggregates used during the construction. The current findings would be beneficial for understanding the sulfate-attack mechanism as well as for future prevention against sulfate attack during construction. © 2015 International Union of Crystallography.